Rolling mill for thin strips

ABSTRACT

BENDING OF A WORKING ROLL IN A ROLLING MILL FOR METAL STRIPS IS PREVENTED BY BACKING THE WORKING ROLL ITSELF OR A BACKING UP ROLL FOR THE WORKING ROLL BY MEANS OF A RUBBER CUSHION CONFINED IN A RECESS OF A RIGID RECEPTACLE BY A PRESSURE TRANSMITTING TROUGH MEMBER MOVABLE INWARDLY AND OUTWARDLY OF THE RECESS AND BLOCKING THE OPEN SIDE OF THE SAME. THE TROUGH MEMBER CONFORMINGLY RECEIVES THE CENTROL PORTION OF THE WORKING ROLL OR BACKING-UP ROLL OVER ALL OR MOST OF THE AXIAL LENGTH OF THE LATTER, AND THE RUBBER CUSHION DISTRIBUTES THE ROLLING PRESSURE UNIFORMLY OVER THE AXIAL LENGTH OF THE ENGAGED ROLL PORTION.   D R A W I N G

' F999, 1971 ELAN 3,591,241I

' ROLLING-M1919 Fon THIN STRIPS 4 Sheets-Sheet 1 Iv 'iled march 11,; 1969 y P. BLAIN I ROLLING MILL FOR THIN STRIPS Fned umh 11, 1969 Fig.7

4 Sheets-Sheet 4 United States Patent O 3,561,241 ROLLING MILL FOR THIN STRIPS Paul Blain, Saint-Germaiu-en-Laye, France, assignor to Institut de Recherches de la Siderurgie Francaise, Saint- German-eu-Laye, France Filed Mar. 11, 1969, Ser. No. 806,218 Claims priority, application France, Mar. 13, 1968, 143,520; Feb. 14, 1969, 6,903,583 Int. Cl. B21b 29/00 U.S. Cl. 72-201 8 Claims ABSTRACT F THE DISCLOSURE Bending of a working roll in a rolling mill for metal strips is prevented by backing the working roll itself or a backing up roll for the working roll by means of a rubber cushion confined in a recess of a rigid receptacle by a pressure transmitting trough member movable inwardly and outwardly of the recess and blocking the open side of the same. The trough member conformingly receives the centrol portion of the working roll or backing-up roll over all or most of the axial length of the latter, and the rubber cushion distributes the rolling pressure uniformly over the axial length of the engaged roll portion.

This invention relates to rolling mills, and particularly to an improved compensating mechanism for preventing defects in metal strips due to the effects of the rolling pressure on the rolls.

When wide and thin strips are to be prepared from heavier material by rolling, notably when they are as thin as 0.2 millimeter, serious difliculties are encountered. For various reasons, and particularly because it is difficult to distribute the rolling pressure over the length of the Working roll, the stretching of the metal is not uniform over the width of the strips. Consequently, the rolled strip is not even and folds may be formed when entering the cylinders whereby breakage occurs. In certain cases, the fact that the stretching is not uniform makes it impossible to roll the material.

All attempts to overcome these difficulties by varying the cross section of the working rolls over their length in order to compensate for the mill spring, which is greater at the center of the rolls than towards the roll necks, have been partly successful only, and measures proposed for preventing the deformation of the rolls were not found practical heretofore.

The primary object of the instant invention is the provision of a compensating arrangement for a strip rolling mill which practically distributes the pressure uniformly over the operating length of the rolls, yet is simple in its structure, and capable of maintenance-free operation over an extended period of time.

In one of its basic aspects, the invention provides a practically rigid receptacle with a recess in which a cushion of solid material is conformingly received, which transmits pressures hydrostatically over the operating length of the roll, the material being either elastomeric or semi-fluid. A pressure transmitting member engages the cushion in the recess of the receptacle and substantially completely blocks the open side of the recess. It moves inwardly and outwardly of the recess through the open side of the latter and has a concavely arcuate face directed outwardly of the recess and constituting a trough. An axial portion of one of the working rolls or backingup rolls of the mill is conformingly received in the trough.

Other features, additional objects and many of the attendant advantages of this invention will readily become apparent as the sarne becomes better understood by reference to the following detailed description when considered in connection with the appended drawing in which:

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FIG. l shows a rolling mill equipped with the compensating device of the invention in fragmentary, frontelevational view;

FIGS'. 2 and 3 respectively show the mill of FIG. 1 in side elevational section on the lines II-II and III-III;

FIGS. 4 and 5 show modifications of the mill of FIG. l in corresponding views;

FIG. 6 shows yet another modified mill according to this invention in a view corresponding to those of FIGS. 2 and 3; and

FIG. 7 illustrates a further modified mill in fragmentary side elevation, and partly in section.

Referring now to the drawing in detail, and initially to FIGS. 1 to3, there is shown only as much of an otherwise conventional rolling mill for very thin strip as is needed for an understanding of this invention. Only the bottom working roll 1 of the mill is seen in FIG. 1. It is a cylindrical body of steel without necks that is conformingly received over the lower third of its circumference in a relatively thin-Walled trough 2 of fiber-reinforced plastic. This material is commonly used in rolling mill plants. The trough 2 is a circumferential segment of a hollow cylinder whose axial edges are enlarged for greater stiffness.

The trough 2 is backed by a molded rubber cushion 3 and practically completely blocks the open side of a recess in a heavy metal base 4 which provides a conforming receptacle for the rubber cushion. The trough 2 transmits the rolling pressure from the roll l1 to the cushion 3 and may move inwardly of the recess in the receptacle 4 under the rolling pressure, thereby compressing the nubber cushion 3 which is much softer and more resilient not only than the receptacle 4, but also than the pressure transmitting trough 2.

Extrusion of the rubber cushion 3 from the receptacle 4 along the enlarged axial edges of the trough 2 under the rolling pressure is prevented by conforming engagement of the trough edges with corresponding ilat faces of the metal base 4, and extrusion of the cushion between the radial end faces of the roll 1 and the wall of the base 4 is prevented by a gasket 5 which is a segment of a flat ring of the same material as the trough 2, interposed between the radial faces of the cylinder 1 and the base 4 and having a cylindrically arcuate ange centered in the axis of rotation of the roll 1 and contiguously interposed between the axial ends of the trough 2 and the rubber cushion 3.

The rubber chosen for the cushion 3 is of such hardness that it will distribute the rolling pressure substantially uniformly like a non-compressible liquid over all walls of the cavity in the receptacle 4 and the trough 2 while lacking the fluidity of a liquid which would make it impractical to confine the cushion in the manner required for its continued operativeness.

The pressure in the rubber or elastomer, resulting from the forces exerted on the roll, is distributed uniformly over its entire volume, and the reaction on the roll is accordingly exactly the same over the entire working length of the roll. The pressure exerted on the strip is consequently substantially the same over the entire width of the srtip Whatever may be the extent of yielding in various pieces. It can easily be seen that it is possible in this Way to obtain a uniform reduction of thickness of the rolled product over its entire Width.

The bottom working roll k1 cooperates with a top Working roll 7 of greater diameter during the rolling of a strip in a known manner, as is indicated in FIG. 2. The top working roll 7 is driven in a conventional manner, not shown.

The compensating device of the invention is equally the friction, in particular on starting up, between the roll and the trough is too great. The roll 8 is partly received in a plastic trough 2 having integral radial anges of which only one is seen in FIG. 4. In this figure, it can be seen in particular that the trough 2' is made of one piece, having a semicircular opening 10 to permit the passage of the neck 9. The remaining pieces have been given the same references as in the preceding figure.

If the material to be rolled is narrower than the axial length of the rolls, the compensating device of the invention may be limited to a portion of a roll approximately equidistant from the two axial ends of the roll, as is shown in FIG. 5. It can be seeen that, in this arrangement, the cushion 3 takes up in length only exactly the width of the rolled strip 12. The rolling pressure will be uniformly distributed over the entire width of the strip and the strip will receive a constant reduction in thickness. As the roll is not subjected to stresses at the ends it cannot yield in `a damaging way. At 13a and 13b openings made in the base 4 are shown which allow the ends of the roll to pass through.

The portions of the roll 11 not directly subjected to the rolling pressure are not backed by the cushion 3, and do not need such backing. The ends of the roll, not themselves seen in FIG. 4, may or may not be equipped with necks, and the roll may or may not be driven, as it is evident from FIGS. 1 and 4 respectively.

The rolling pressure need not be transmitted directly by a trough from a working roll to a rubber cushion, as has been shown in FIGS. 1 to 5, but a backing-up roll may be interposed between the working roll and one or more rubber cushions.

FIG. 6 partly illustrates a rolling mill in which a bottom working roll 14 and a larger top working roll 15 shape a strip 16 therebetween, the bottom working roll being mounted on two backing-up rolls 17, 18. The rolling pressure is transmitted from the backing-up rolls to respective rubber cushions 3a, 3b in recesses of a common metal base 4a by respective plastic troughs 2a, 2b in the same manner as described hereinabove. This arrangement could be preferred in cases when the wear on the rolls in contact with the trough would be heavy and could mark the sheet.

The trough which transits rolling pressure from the rolls of the mill to a confined rubber cushion may be made of any relatively rigid material having a low coefficient of friction in contact with the metal that is being rolled, and it need not necessarily be as thin-walled as has been shown in FIGS. 1 to 6.

FIG. 7 shows a bottom working roll 1a which is supported on a pressure-transmitting, rectangular slab 19 of copper or copper-base alloy whose top face is hollowed out to form a trough. A silver coating 20 about 2 millimeters thick, for instance a thin silver sheet properly brazed, covers the trough face which is approximately cylindrical about an axis perpendicular to the plane of FIG. 7. The slab 19 is slidably received in a conforming recess of a rigid metal base 22 and blocks the open side of the recess, thereby conning a rubber cushion 21 in the same. Gaskets 23, which are rails of L-shaped cross section, prevent extrusion of the rubber between the opposite walls of the slab 19 and of the base 22.

While silver and steel have a low coefficient of friction, and do not tend to seize when in contact, lubrication at the interface of the steel roll 1a and of the trough facing 20 is provided by water supplied through pipes 24 and controlled by spigots 25 which splash the water on the exposed surface of the roll 1a, two 'water supply systems being provided for clockwise and counter-clockwise rotation of the roll 1a respectively.

The viscosity of water and its ability of forming a continuous lubricant lm under pressure are inversely related to the water temperature, and it is, therefore, important to maintain the water lm at a temperaure as close to the freezing point as possible, in spite of the risk of said water being heated up by reason of the considerable pressure forces exerted by the system. The copper slab 19 is, therefore, provided with two refrigerant ducts 26 connected to a mechanical refrigeration system, not itself shown, and normally filled with a fluorocarbon refrigerant during operation of the mill. The ducts are received in elongated notches 27 formed in the bottom face of the slab y19, and closed after insertion of the ducts 26 by means of brazed-copper bars 28.

The ducts 26 are angularly offset about 30 in opposite directionsfrom a vertical plane through the axis of curvature of the roll 1a, and axially elongated, radial depressions 29 in the trough face 20 of the slab 19 are radially aligned with the ducts 26. The depressions 29 thus are colder than the remainder of the trough face, and the refrigerant in the ducts 26 is kept at a temperature low enough to cause the water in the depressions 29 to freeze. Cooling is therefore most effective in the lowermost portion 30 of the trough where the pressure is highest during rolling of a strip 31 between the bottom working roll 1a and a top working roll 32.

Rubber and other elastomeric materials, such as synthetic rubbers and plasticized resin compositions more commonly thought of as plastics, are preferred cushion materials, but at least some of the advantages of the nvention can be achieved with cushions made of other soft or semi-fluid materials, such as stiff grease compositions whose viscosity is high enough so as not to create leakage problems.

Water, particularly when refrigerated, is an adequate and preferred lubricant with metallic trough members, but soluble oil may be incorporated therein, and other lubricant additives will readily suggest themselves to those skilled in the art. The plastic troughs, the main object of which is to improve the sliding contact with the roll, described with reference to FIGS. 1 to 6, may be of synthetic resin, reinforced with textile fibers. This material, such as Celoron or Textolite, is commonly used in rolling mill plants for making the roll neck bushings.

What is claimed is:

1. In a rolling mill for thin strips having a plurality of rolls arranged for simultaneous rotation and for transmitting rolling pressure to each otherand to a piece of metal passing between two of said rollers, and compensating means for preventing defects in the rolled metal due to the effects of the rolling pressure on the rolls, the improvement in the compensating means which cornprises:

(a) a substantially rigid receptacle formed with a recess, having an operating length substantially equal to the width of the strips,

(1) said recess having an open side;

(b) a cushion of material conformingly received in said recess, said material being elastomeric or semifluid, which transmits pressures hydrostatically over the said length;

(c) a pressure transmitting member engaging said cushion in said recess and substantially completely blocking said open side,

(1) said member being movable inward and outward of said recess through said open side, and having a concavely arcuate face directed outwardly of said recess,

(2) said face constituting a trough,

(3) an axial portion of one of said rolls remote from the axial ends of said roll and substantially equal to said length being conformingly received in said trough.

2. In a mill as set forth in claim 1, said pressure transmitting member essentially consisting of reinforced plastic or metal.

3. In a mill as set forth in claim 1, said pressure transmitting member essentially consisting of metal, said compensating means further comprising means for maintaining a lm of liquid lubricant between said pressure transmitting member and said one roll, and cooling means in thermal contact with said pressure transmitting member for controlling the temperature of said ilm.

4. .In a millas set forth in claim 3, said pressure transmitting member mainly consisting of copper, said face thereof essentially consisting of silver, said one roll consisting of steel, and said cooling means including a refrigerantduct in said pressure transmitting member.

5. In a mill as set forth in claim 4, said face of the pressure transmitting member being formed with a depression therein aligned with said duct.

6. In a mill as set forth in claim 4, said means for maintaining a iilm of liquid lubricant including a supply of Water, and means for controlling the application of said water to the surface of said one roll.

7. In a mill as set forth in claim 1, said trough being much longer in the direction of the axis of said one roll References Cited UNITED STATES PATENTS 977,725 12/1910 Gautschi 72-201 3,350,909 11/1967 DeMasi 72-242 LOWELL A. LARSON, Primary Examiner U.S. Cl. X.R. 

